1. Field of the Invention
The present invention relates to a sheet with movable contacts and a sheet switch using the same, which are for use in operating panels of various electronic devices for example.
2. Description of the Related Art
A conventional structure of a sheet with movable contacts and that of a sheet switch are shown in FIGS. 5 and 6. FIG. 5 is a sectional view of the sheet with movable contacts and FIG. 6 is a sectional view of a sheet switch using the sheet with movable contacts.
In those figures, the sheet with movable contacts is made up of movable contacts 25 formed in a dome shape using metal, a sheet 21 formed by an insulating film, the sheet 21 covering upper surfaces of the movable contacts 25 and having an adhesive 23 applied to a lower surface thereof, and a separator sheet 26 affixed to the lower surface of the sheet 21 to close lower surfaces of the movable contacts 25, the separator sheet 26 being formed by paper or an insulating film.
The domed upper surfaces of the movable contacts 25 are covered with and fixed to the adhesive 23 which is applied to the lower surface of the sheet 21. The separator sheet 26 affixed to the lower surface of the sheet 21 is for preventing corrosion of the movable contacts 25 caused by gases contained in air or for preventing the adhesion of foreign matters to the movable contacts, during storage or transport of the sheet. The separator sheet 26 can be peeled off.
A small hole 25a is formed in a central portion of each movable contact 25, and on the lower surface portions of the sheet 21 which surround the small holes 25a there are formed sheet exposed portions 21a with the adhesive 23 not applied thereto. Since the small hole 25a is formed in the central portion of each movable contact 25, the movable contact comes into contact with a central fixed contact to be described later at an end face of an outer periphery of the small hole formed centrally of the movable contact 25, so that the contact of the movable contact with the central fixed contact is further ensured.
Since the sheet exposed portions 21a free of the adhesive 23 are formed on the lower surface portions of the sheet 21 which surround the small holes 25a of the movable contacts 25, it is possible to prevent the entry of the adhesive 23 onto inner surfaces of the movable contacts from the small holes 25a.
As shown in the figures, the sheet 21 is provided with sheet exposed portions 21b with the adhesive 23 not applied thereto, in the vicinity of lower ends of outer peripheral portions of the movable contacts 25, whereby it is also possible to prevent the entry of the adhesive 23 from the lower ends of the outer peripheral portions of the movable contacts 25.
The sheet switch is made up of the above sheet with movable contacts and a circuit board 27 provided on an upper surface thereof with central fixed contacts 29 and outer fixed contacts 28. In a removed state of the separator sheet 26 from the sheet with movable contacts, the movable contacts 25 are affixed onto the circuit board 27 using the adhesive 23 applied to the lower surface of the sheet 21 in such a manner that lower ends of the outer peripheries of the movable contacts 25 are respectively brought into abutment with the outer fixed contacts 28 and that central portions thereof are opposed to the central fixed contacts 29.
In the above structure of the sheet switch, when an operating portion of a rubbery or resinous push-button (not shown) disposed above the sheet switch is depressed, the associated movable contact 25 is depressed by a depressing portion formed on a lower surface of the operating portion via the sheet 21 and is inverted, so that its central portion comes into abutment against the associated central fixed contact 29 on the circuit board, whereby the central fixed contact 29 and the associated outer fixed contact 28 on the circuit board 27 are electrically connected with each other. Upon release of the depressing force imposed on the push-button, the central portion of the movable contact 25 is disconnected from the central fixed contact 29 with an elastic restoring force of the movable contact.
In the above conventional structures of the sheet with movable contacts and the sheet switch, however, the movable contacts 25 are covered with and fixed to a single sheet 21 of an insulating film with the adhesive 23 applied to the lower surface of the sheet, so when the sheet with movable contacts is affixed onto the circuit board 27 and when any of the domed movable contacts 25 located near the outer periphery of the sheet 21 is depressed, the air present within the dome of the movable contact is forced out and causes an end portion of the sheet to float, thus giving rise to the problem that dust enters through the floating end portion and causes an incomplete state of contact.
Moreover, the portions of the sheet 21 which surround the domed movable contacts 25 are fixed with the adhesive 23, so when any of the movable contacts 25 is depressed, the air present within the dome of the depressed movable contact cannot escape anywhere, thus giving rise to the problem that the operation feeling is deteriorated.
Further, it is required that the adhesive 23 be applied to the lower surface of the sheet 21 by such a printing method as masking so as to prevent the adhesive from being applied to the small holes 25a formed respectively in the central portions of the movable contacts 25, thus causing the problem that the production becomes complicated and the manufacturing cost increases.